Glyphosate is a well characterized herbicide used to inhibit the growth of unwanted plants, such as grasses and weeds. Briefly, glyphosate is a non-selective systemic herbicide that prevents the synthesis of essential amino acids. Glyphosate is commonly used in the form of a salt, for example, potassium, trimethylsulphonium, isopropylamine, sodium, ammonium, diammonium, dimethylamine and triethanolamine as well as mixtures of these salts.
Glyphosate is often sold as concentrated salt or acid formulations configured to be diluted for application. For example, Touchdown Total® herbicide (Syngenta) is a commercial preparation of glyphosate in its potassium salt form, containing 500 grams of glyphosate (acid equivalent) per liter of water. Touchdown Total® herbicide is typically diluted in water to create a concentration suitable for application. Herbicidal application rates, in terms of the glyphosate acid equivalent may vary depending on, for example, species, age, stress, time of year, crop rotation, biotype, etc., but common rates include 560 g a.e./ha, 1120 g a.e./ha, and 1680 g a.e./ha.
The use and importance of glyphosate has increased in recent years because a variety of crop plants have been genetically transformed or selected to exhibit resistance to glyphosate. For example, glyphosate tolerant corn, glyphosate tolerant cotton and glyphosate tolerant soybeans may be treated with glyphosate with little risk of crop damage, resulting in increased yields due to decreased weed competition. Despite such benefits, one problem associated with the increased use of glyphosate is the development of glyphosate resistant weeds. Glyphosate resistant weeds can develop through natural selection in the field, as biotypes exhibiting some level of resistance outcompete herbicide-susceptible biotypes. Herbicide resistance is conferred to subsequent generations, where it may undergo additional selective pressure. The result is a weed population that can survive otherwise lethal doses of herbicide and negatively impact crop yield. One way to reduce the development and spread of glyphosate resistant weeds is to administer at least one other herbicide in addition to glyphosate to inhibit the glyphosate resistant weeds.
Mixes of two or more herbicides are commonly prepared by the grower in a process known as tank mixing. In tank mixing, typically, two or more concentrated formulations are dissolved, emulsified and/or suspended in a larger volume of water. One tank mix useful, for example, for treating or preventing glyphosate resistant weeds is prepared by tank mixing Touchdown Total® herbicide with Flexstar® herbicide (Syngenta). Flexstar® herbicide is a commercial preparation of fomesafen in its sodium salt form. Fomesafen is a known herbicide used to inhibit unwanted plant growth, and is typically used for post-emergence control of weeds, e.g., broad leaved weeds, in soybean plants. Fomesafen has the following structure, in acid form:

In addition to being useful for controlling and preventing resistant weed biotypes, herbicidal mixes are also useful for treating wild type weeds, for example, when a variety of different weeds are growing together or when trying to reduce the application rates of specific active ingredients. Mixing, however, is sometimes problematic.
For example, even in dilute tank mixes, compatibility between glyphosate and other herbicides is sometimes difficult to achieve. Further, when higher concentrations of glyphosate and another electrolytic herbicide are prepared, as when trying to make commercial premixes, the likelihood of compatibility problems is greatly increased. For example, in concentrated commercial mixes containing glyphosate and another electrolytic herbicide, phase separation, formation of solid precipitates, or other formulation failures can occur. Additionally, in some instances, tank mixing may result in crop phytotoxicity and/or herbicide antagonism or reduced weed control efficacy. Further, in some instances, herbicide mixes may formulate initially, but might not be suitable for storage and transport.
Various embodiments of the invention are directed to various combinations of these, and additional, problems.